1) Field of the Invention
The present invention relates to a technology for determining a cause of an inability of processing a picked-up image.
2) Description of the Related Art
Some of the techniques that have been developed recently enable preventing running vehicles getting into accidents and assisting running and parking of the vehicles. According to these techniques, an imaging device is installed on a vehicle, and image information is collected with the imaging device on the surrounding of the vehicle while the vehicle is running. The image information is processed and used to predict accidents and prevent the vehicle getting into the accident. The imaging device is generally a camera. The amount of light that enters the cameras changes with brightness of the sun, climate, and shadows of objects so that a light source in the camera continuously adjusts itself accordingly. However, sometimes the shutter speed and the aperture control cannot follow the speed of adjustments of the light source. A density gradation loss in bright parts (hereinafter, a “bright density loss”) or a density gradation loss in dark parts (hereinafter, a “dark density loss”) occurs, which is beyond control of the shutter speed and the aperture.
When the camera control cannot follow the speed of changes in light source conditions or when a bright density loss or a dark density loss occurs in picked-up images that is beyond control of the camera, the picked-up image signals cannot be processed properly. In this case, it is necessary to determine that the camera has picked up the image under an abnormal state, and therefore, the image should not be processed. Assuming that the camera itself is not down, if an image is picked under an abnormal state, an image under a normal state can be picked up after a lapse of certain time. However, if the camera is down, an image in a normal state cannot be picked up. Therefore, a technique to determine whether the camera is down is required.
Moreover, a running vehicle may change directions at a high speed so that light source conditions change rapidly. Therefore, images need to be processed at a high speed. It is necessary to quickly determine and notify the vehicle driver about whether the abnormal states of picked-up images are due to a temporary environmental change or due to a trouble in the camera itself.
A conventional video camera exposure controlling device has been described in Japanese Patent Application Laid-Open No. H5-122600. This video camera exposure controlling device has a high-luminance clip circuit that sets a luminance signal of a picked-up image to the same luminance signal when the luminance signal of an input image is a preset clip level or higher. The high-luminance clip circuit changes a clip level between a low clip level to obtain proper photometric information in a backlit scene and a high clip level to obtain proper photometric information in a photographic scene other than a backlit scene. The exposure controlling device controls iris based on the photometric information from the luminance information that passes through the high-luminance clip circuit. A clip level is changed between the low clip level and the high clip level by gradually delaying the clip level or with a certain time delay.
According to the conventional technique, it is possible to obtain proper photometric information in a backlit scene by setting a luminance signal of a preset clip level or higher to the same luminance signal. However, it is not possible to determine whether the luminance signal of a preset clip level or higher is due to a temporary environmental change or due to a trouble in the camera itself.